The upcoming Interface Types spec for WebAssembly was thinking to not support WTF-16 string format, which means any Wasm modules (for example those written in AssemblyScript, a web-inspired language) passing strings from one side to the other (f.e. from Wasm to JS) will experience two things:

- an extra performance cost due to format conversion at the boundary,

- as well as negative implications on security and data integrity,

thus making this a loss for the web if Interface Types will not be fully compatible with the web (JavaScript) by default.

Hope that sums it up in one sentence. :)